Our prior work has identified neuropeptide-containing or peptidergic neurons in the retina of various vertebrate species. The objective of the proposed research is to provide a detailed analysis of peptidergic neurons in mammalian (monkey and rabbit) and avian retinas. These studies will utilize radioimmunoassay, light and electron microscopic immunohistochemistry and receptor site autoradiography to provide a description of these retinal neurons. These studies have four major objectives; (1) Peptidergic cell populations will be identified and characterized on the basis of (A) their morphological appearance (light and electron microscopic) and (B) their regional distribution in the retina. (2) An evaluation will be made of the co-occurrence of two neuropeptides or a neuropeptide and a "conventional" neurotransmitter within the same cell type. (3) The location of neuropeptide binding sites (receptor sites) will be determined using specific radiolabeled neuropeptides and neuropeptide ligands. (4) The ontogeny of peptidergic neurons and their receptor sites will also be determined. The goal of these studies, is to further our understanding of peptidergic neurons within the vertebrate retina. In view of previous data, which have localized morphologically distinct peptidergic amacrine cells, the proposed studies will further our understanding of amacrine cells and may provide insight as to their role in retinal processing. More generally, these studies could contribute to our understanding of the role of neuropeptides in the central nervous system.